1. Field of the Invention
The invention relates to a method and a device for video-based observation and measurement of the lateral environment around a road vehicle.
2. Related Art of the Invention
Depending on the application, initial driver assistance systems which are commercially obtainable require a compromise between the resolution of the scanning and the size of the sensed area. For example, the radar sensor system for an ACC application must be restricted to several degrees of the sensing area in the horizontal direction while for a parking assistance function only a short range and resolution can be implemented when sensing the environment next to the vehicle using ultrasonic sound. Conventional video-based systems provide a good compromise between the resolution and the sensing range but generally do not supply any direct distance information.
Systems which use the vehicle's own movement to obtain three-dimensional environment data from two-dimensional depth of profile data are presented, on the one hand, in documents U.S. Pat. No. 4,179,216 A1 and U.S. Pat. No. 4,490,038 A1 for monitoring railway tunnels and fault-free operations on rail routes and, on the other hand, in U.S. Pat. No. 5,278,423 A1 in connection with the selective recovery of pesticides and the sensing of the stock of trees in plantations. In all these systems, a three-dimensional image of the environment is generated in a data processing unit by arranging a set of successive distance profiles in a series. In order to be able to determine the distances between the individual, sequentially recorded profiles, in each case distance sensors are arranged on the wheels of the vehicles fitted with the systems.
A device for sensing the position of an agricultural vehicle which is fitted with a scanning sensor is described in U.S. Pat. No. 5,809,440 A1. Here, the track of the vehicle is followed by means of a global navigation system (GPS). However, since the scanning optical sensor which is used for recording images of the plant cover does not supply any distance information, only a two-dimensional cartography of the underlying surface can be obtained by arranging the sensor information items serially.
Driver's assistance systems are increasingly employing stereoscopic camera systems by means of which it is possible to determine computationally the object width on the basis of the known geometric arrangement of the pair of cameras used. In stereoscopic image processing, an object is scanned from different directions using a pair of cameras. The distance between the stereoscopic camera system and the object is then determined taking into account the camera positions and orientations as well as the camera parameters based on the principle of triangulation.
DE 199 26 559 A1 discloses a method and a device for detecting objects in the environment of a road vehicle. In the method which is presented, the distance from a moving vehicle is calculated by evaluating stereoscopic image pairs and properties of the detected object are determined. In particular, a distance-based segmentation of images is carried out by means of stereoscopic image processing. An object detection process is then carried out in the segment image areas.
A similar system is known from EP 108 72 57 A2, which describes an arrangement for mounting a stereoscopic camera system in a vehicle, which system is used for calculating a three-dimensional distance distribution for an object under consideration. However, when used in road vehicles such stereoscopic image processing systems which are known from the prior art can be used only to a limited degree since the position and orientation of the camera has to be very precise and has to be adjusted with a large amount of effort. Furthermore, such an arrangement is not often robust enough for everyday use and a wide variety of road conditions.